Helmet antenna

ABSTRACT

An antenna having a configuration which may be positioned entirely within a conventional helmet formed of a dielectric material. The antenna is comprised of a loop-type, conductive member having a capacitance connected between the ends thereof, and a pair of elongated conductive elements extending from the ends of the loop-type member and diverging outwardly with respect to each other. The capacitance includes a fixed capacitor connected in parallel with a short length of coaxial cable which may be trimmed off to alter the total capacitance between the ends of the loop-type conductive member to thereby resonate the antenna.

United States Patent [72] Inventor John Altmayer Euclid, Ohio [21] Appl. No. 735,915 [22] Filed June 10, 1968 [45] Patented June 1,1971 [73] Assignee New-Tronies Corporation Cleveland,0hio

[54] HELMET ANTENNA 4 Claims, 5 Drawing Figs.

[52] U.S. Cl 343/718, 343/726, 343/743, 343/744, 343/750 [51] Int. Cl 110lq 1/44, 1-l0lq 7/00, HOlq 9/14 [50] Field of Search 343/718, 720, 726, 743, 744, 745, 748, 850, 862, 864, 872, 873

[56] References Cited UNITED STATES PATENTS 2,614,220 10/1952 Doemer 343/866X 2,169,377 8/ 1939 Walter 343/862X 2,469,209 5/1949 Scheldorf 343/744 2,657,312 10/1953 Saranga 343/726(UX) 2,666,846 1/1954 Davis 343/748X 2,842,765 7/ 1958 Schmitt 343/726 2,904,645 9/1959 Sarles 343/718X 3,134,074 5/1964 Litke 343/718X 3,199,108 8/1965 Munk 343/720X 3,266,042 8/1966 Mahoney ct a1. 343/720X Primary Examiner-Herman Karl Saalbach Assistant Examiner-William H. Punter Attorney-Meyer, Tilberry and Body ABSTRACT: An antenna having a configuration which may be positioned entirely within a conventional helmet formed of a dielectric material. The antenna is comprised of a loop-type, conductive member having a capacitance connected between the ends thereof, and a pair of elongated conductive elements extending from the ends of the loop-type member and diverging outwardly with respect to each other. The capacitance includes a fixed capacitor connected in parallel with a short length of coaxial cable which may be trimmed off to alter the total capacitance between the ends of the loop-type conductive member to thereby resonate the antenna.

mmmnm -3582,951

SHEET1UF2 INVENTOR.

JOHN ALTMAYER BY Maya, 7% 8 Body ATTORNEYS PATENT-ED JUN 1 I97! SHEET 2 [1F 2 INVENTOR.

JOHN ALTMAYER ATTORNEYS HELMET ANTENNA This invention relates to the art of antennas and, more particularly, to antennas of a generally loop-type configuration.

The invention is particularly applicable to the art of antennas for use with portable transmitters and will be described with particular reference thereto; although it is to be appreciated that the invention has a broader application, such as in any application where space requirements are limited.

In the past, portable transmitters employed vertical antennas which had to be maintained in a position free from contact with the person operating the transmitter, or other objects which would tendto ground the antenna, and thereby interfere with the signal being radiated from the antenna. Such an antenna is inherently inconvenient and dangerous for the person using the transmitter.

More recently, such antennas have been mounted on the top portion of a helmet and were fed with a coaxial cable; however the conductive antenna element created a potentially dangerous hazard to the operator in the event this conductive element came in contact with certain objects such as overhead power lines.

A further problem that exists with short, compact antennas is that such antennas generally have a relatively low radiation efficiency because of the difficulty in tuning the antenna to resonance at the operating frequency, and in matching the input impedance of the antenna to the characteristic impedance of a coaxial cable transmission line, thereby resulting in a high standing-wave ratio and a substantial loss of transmitted power.

The present invention contemplates a new and improved antenna which overcomes all of the above referred-to problems, and others, and provides a small, compact antenna having a high radiation efficiency.

in accordance with the present invention an antenna is provided having a loop-type conductive member, a capacitance connected, between the ends thereof to resonate the antenna at a given operating frequency, and a pair of elongated conductive elements extending from the ends of the loop-type conductive member and diverging outwardly with respect to each other.

In accordance with a more limited aspect of the present invention, the capacitance includes a fixed capacitor being connected in parallel with a short length of coaxial cable. The capacitance of the coaxial cable as manufactured is slightly in excess of that required to resonate the antenna, such that the cable may be trimmed off to bring the antenna into resonance at the operating frequency.

Further, in accordance with the present invention an antenna is provided having a loop-shaped configuration with a tuning means, and which may be positioned entirely within a conventional helmet formed of a dielectric material.

The primary object of the present invention is to provide a loop-type antenna in which the entire antenna or radiating element is located within the helmet.

Another object of the present invention is to provide a looptype antenna with increased radiation efficiency provided by a pair of diverging radiating elements extending from the loop portion of the antenna.

Another object of the present invention is to provide a small, compact antenna with relatively high radiation efficiency.

A still further object of the invention is to provide a helmet liner having an antenna or radiating element mounted directly thereon, and which is easily removable from the helmet for adjustment of the resonant frequency of the antenna.

Another object of the present invention is to provide a looptype antenna having a means for resonating the antenna to the desired frequency of operation and a means for accurately matching the input impedance of the antenna to the characteristic impedance of the coaxial cable transmission line.

A still further object of the invention is to provide a lightweight, portable antenna which may be used by a person without the necessity of carrying the antenna by hand.

These and other objects and advantages of the invention will become apparent from the following description of the preferred embodiment of the invention as read in connection with the accompanying drawings in which:

FIG. 1 is a pictorial drawing illustrating generally the front portion of one embodiment of the invention;

FIG. 2 is a pictorial drawing illustrating generally the rear portion of the embodiment shown in FIG. I;

FIG. 3 is a schematic illustration of the antenna system of the embodiment shown in FIG. 1

FIG. 4 is an elevational view illustrating the circuit arrangement of the embodiment as shown in FIG. 1; and,

FIG. 5 is a cross-sectional view taken generally'at line 55 of FIG. 2.

Referring now to the drawing, wherein the showings are for the purpose of illustrating the preferred embodiment of the invention, and not for purposes of limiting the same, FIG. 1 illustrates one embodiment of the invention which takes the form of a helmet-liner l0, loop-type conductive member 12, a pair of elongated conductive elements 18, 20, fixed capacitor 22, and a short length of coaxial cable 24.

In the preferred embodiment the conductive member 12 is constructed of a thin strip of conductive material, such as copper, and takes the form of a generally C-shaped configuration having ends or terminals 14 and 16, located in spaced adjacent relationship with each other. Connected to the terminals l4, 16, of the conductive member 12 are a pair of elongated conductive elements 18, 20. Conductive elements 18, 20, are preferably constructed of a material similar to that of the loop-type member 12, extend from the terminals 14 and 16, and diverge outward with respect to each other, thereby forming a generally V-shaped configuration having an apex located generally at the terminals 14 and 16 of the loop-type member 12. Asillustrated in FIGS. 1, 2, and 5, the pair of elongated conductive elements 18, 20, extend toward the inside of the loop-type configuration formed by the conductive member 12, and extend out of a plane defined by the conductive member 12 and lie in a surface formed by the upper portion of the helmet liner 10.

Preferably, the helmet-liner 10 takes generally the configuration of the upper portion of a persons head and is comprised of an inner layer 26, and an outer layer 28 which encapsulates the C-shaped conductive member 12 and the elongated conductive element 18, 20. In the preferred embodiment of the invention, the inner layer 26 and the outer layer 28 are constructed of a thin, dielectric, flexible, lightweight material, such as vinyl sheet, although other suitable materials within the scope of the invention are contempiated.

The coaxial cable 24 includes an outer conductor 30 and a center conductor 32 which are connected to the terminals 14, 16, of the loop-type conductive member 12, respectively. The fixed capacitor 22 is connected in parallel with the conductors 30, 32, of the coaxial cable 24 and also across terminals l4, 16 of the loop-type member 12.

Coaxial cable 24 is employed as a variable capacitive element and is comprised of a coaxial cable being of a length which is slightly in excess of that required to bring the antenna into resonance, such that the length of the coaxial cable may be trimmed off to accurately bring the antenna into resonance. The capacitance of the coaxial cable 24 is additive to that of the fixed capacitor 22, since the two capacitive elements are connected in parallel. As the length of the coaxial cable 24 is decreased in the process of tuning the antenna, the effective capacitance between the terminals 14, 16, decreases accordingly.

Having now described the major radiating elements of the antenna, a description is now presented as to the manner in which the input impedance of the antenna is matched to the characteristic impedance of the coaxial cable transmission line 36. As shown in FIGS. 3 and 4, a gamma-match arrangement is employed to obtain a feed-point impedance of the antenna equal to the characteristic impedance of the coaxial cable 36. The impedance matching arrangement is comprised of a matching section 38 and a shorting strap 40 connected between one terminal of the matching section 38 and the looptype conductive member 12. The matching section 38 is comprised of an elongated conductive member being substantially parallel to the loop-type member 12. Matching section 38 and shorting strap 40 are preferably constructed of a material similar to that of the loop-type conductive member 12. Coaxial cable 36 includes an outer shield 42 which is connected to the center point of the loop-type member 12, and an inner conductor 44 which is connected to the end of matching section 38.

As illustrated in FIG. 5, the outer layer 28 of the helmet liner 10 provides a covering for the major portion of the thin conductive elements, i.e. the conductive member 12, conductive elements 18, 20, matching section 38, and shorting strap 30; however, in the preferred embodiment, the fixed capacitor 22 and the coaxial cable 24 remain exposed. Coaxial cable 24 extends in a groove 30 located in the top portion of the helmet liner 10, so that coaxial cable 24 may be trimmed off to accurately tune the antenna to resonance at the operating frequency.

FIG. 5 illustrates the cooperation between the helmet liner l0, and the inner portion of the helmet 48. Preferably, the helmet 48 is of conventional design and is constructed of a strong, dielectric, lightweight material, such as fiber glass although other suitable materials within the scope of the inventions are contemplated. The helmet liner is of a tight fitwithin the helmet 48, and may be retained by this tight fit, or alternatively plastic clips or other dielectric devices may be employed to releaseably retain the liner 10 within the helmet 48.

TUNING THE ANTENNA In manufacturing the antenna of the present invention, the thin conductive elements, i.e. loop-type member 12, matching section 38, shorting strap 40, and elongated conductive elements 18, 20, are cut to lengths which approximately resonate the antenna and provide a match between the input impedance of the antenna and the characteristic impedance of the coaxial cable feedline 36. The thin conductive elements are then mounted on the inner liner 26, and, except for terminals l4, l6, and the connection points for the coaxial cable 36, these elements are completely encapsulated with the outer cover 28. The capacitive elements 22, 24 and coaxial cable feedline 36 are then connected to the thin conductive elements.

When it is desired to tune the antenna to a particular frequency of operation, a S.W.R. meter is connected across the conductors of the coaxial cable 36. An exitation signal of the particular frequency is then applied to the coaxial cable feedline 36 and the short length of coaxial cable 24 is trimmed until a minimum standing-wave ratio is obtained.

While the preferred embodiment of the invention illustrates the loop-type antenna mounted on a helmet liner within a dielectric helmet, it will be appreciated that this antenna may be employed in various other embodiments.

Typical component values and length of elements for one embodiment of the preferred invention, are approximately as follows:

Distance between terminal points 14/16 t. )6 inc Distance between divergent ends of conductive bars 3% inches.

18,20. Distance between conductive bars 18, 20 and con- 2%inches.

ductive loop member 12. Value of fixed capacitor 22- .33 mmfd Coaxial cable 36 The invention has been described in connection with the particular preferred embodiment, but is not to be limited to the same. Various modification may be made without departing from the scope and spirit of the present invention as defined by the appended claims.

I claim:

1. An antenna comprising:

a loop-type conductive member having a pair of terminals located in spaced adjacent relationship with respect to each other;

a capacitance means connected between said pair of terminals;

a pair of elongated conductive elements each being connected to one of said pair of terminals and diverging outwardly with respect to each other; and,

means for applying a radiofrequency signal to said loop-type conductive member, I

said capacitance means comprising a fixed capacitor, and a variable capacitor which takes the form of a length of coaxial cable having an outer braided conductor and a center conductor; said outer conductor being connected to one of said pair of terminals, and said center conductor being connected to the other of said pair of terminals so that as the length of the coaxial cable is decreased the capacitance between said pair of terminals decreases.

2. An antenna as defined in claim 1 wherein said coaxial cable extends generally in a same configuration as said elongated conductive elements.

3. An antenna as defined in claim 2 wherein said conductive member, said pair of conductive elements, said matching member and said shorting member, are comprised of thin copper strip material.

4. In a helmet being formed of dielectric material, an antenna comprising:

a helmet liner being formed of a dielectric material and being of a configuration adapted to fit in close proximity to a head;

a conductive antenna element mounted on and oriented in a superimposed relationship with said helmet line; and,

an outer covering of dielectric material covering said element to thereby provide an outer insulation layer for the antenna element,

said antenna element comprising a thin strip of copper material, including:

a loop-type conductive member having a pair of terminals located in spaced adjacent relationship with respect to each other;

a capacitance means connected between said pairs of terminals;

a pair of elongated conductive elements each being connected to one of said pair of terminals and diverging outwardly with respect to each other; and,

means for applying a radiofrequency signal to said loop-type conductive member,

said means for applying said signal comprising;

elongated impedance matching member being substantially parallel to said conductive member;

said matching member having a first and second terminal;

a shorting member connected between said first terminal of said matching member and said conductive member; and,

a transmission line having a first and a second conductor,

said first conductor being connected to said conductive member, and said second conductive being connnected to said second terminal of said matching member,

said capacitance means comprising a fixed capacitance element, and a variable capacitance element which takes the form of a length of coaxial cable having an outer braided conductor and a center conductor; said outer conductor being connected to one of said pair of terminals, and said center conductor being connected to the other of said pair of terminals so that as the length of the coaxial cable is decreased the capacitance between said pair of terminals decreases. 

1. An antenna comprising: a loop-type conductive member having a pair of terminals located in spaced adjacent relationship with respect to each other; a capacitance means connected between said pair of terminals; a pair of elongated conductive elements each being connected to one of said pair of terminals and diverging outwardly with respect to each other; and, means for applying a radiofrequency signal to said loop-type conductive member, said capacitance means comprising a fixed capacitor, and a variable capacitor which takes the form of a length of coaxial cable having an outer braided conductor and a center conductor; said outer conductor being connected to one of said pair of terminals, and said center conductor being connected to the other of said pair of terminals so that as the length of the coaxial cable is decreased the capacitance between said pair of terminals decreases.
 2. An antenna as defined in claim 1 wherein said coaxial cable extends generally in a same configuration as said elongated conductive elements.
 3. An antenna as defined in claim 2 wherein said conductive member, said pair of conductive elements, said matching member and said shorting member, are comprised of thin copper strip material.
 4. In a helmet being formed of dielectric material, an antenna comprising: a helmet liner being formed of a dielectric material and being of a configuration adapted to fit in close proximity to a head; a conductive antenna element mounted on and oriented in a superimposed relationship with said helmet line; and, an outer covering of dielectric material covering said element to thereby provide an outer insulation layer for the antenna element, said antenna element comprising a thin strip of copper material, including: a loop-type conductive member having a pair of terminals located in spaced adjacent relationship with respect to each other; a capacitance means connected between said pairs of terminals; a pair of elongated conductive elements each being connected to one of said pair of terminals and diverging outwardly with respect to each other; and, means for applying a radiofrequency signal to said loop-type conductive member, said means for applying said signal comprising; elongated impedance matching member being substantially parallel to said conductive member; said matching member having a first and second terminal; a shorting member connected between said first terminal of said matching member and said conductive member; and, a transmission line having a first and a second conductor, said first conductor being connected to said conductive member, and said second conductive being connnected to said second terminal of said matching member, said capacitance means comprising a fixed capacitance element, and a variable capacitance element which takes the form of a length of coaxial cable having an outer Braided conductor and a center conductor; said outer conductor being connected to one of said pair of terminals, and said center conductor being connected to the other of said pair of terminals so that as the length of the coaxial cable is decreased the capacitance between said pair of terminals decreases. 